1. Field of the Invention
The present invention relates generally to a vane pump, and specifically to a vane pump, which can be effectively used in, for example, a fuel vapor leakage check module that checks fuel vapor leakage.
2. Description of Related Art
A known vane pump compresses and discharges fluid by rotating a rotor, which includes vanes and is eccentrically received in a pump chamber of a casing in such a manner that the rotor is connected to a rotatable shaft of a motor. Japanese Unexamined Patent Publication No. 10-90107, which corresponds to U.S. Pat. No. 5,890,474, discloses one such vane pump, which is used in a fuel vapor leakage check module that checks leakage of fuel vapor from a fuel tank and which depressurizes or pressurizes the interior of the fuel tank. In this type of vane pump, a pump flow rate is important since the pump flow rate has a significant influence on the performance of the fuel vapor leakage check module. The pump flow rate can be adjusted by adjusting an amount of deviation of the rotational center of the rotor relative to the center of the pump chamber (i.e., a degree of eccentricity of the rotor relative to the pump chamber).
In one previously proposed vane pump, bolts are installed through a casing and are threadably engaged with a mount of a motor, so that the casing is securely connected to the mount by the bolts. The degree of eccentricity of the rotor and thereby the pump flow rate of the vane pump may be adjusted by loosening the bolts and then moving the casing relative to the mount.
However, the holes of the casing, which receives the bolts, are formed as cylindrical loose holes to allow relative movement of the casing relative to the mount. Thus, the position of the casing relative to the mount can be relatively easily displaced in a radial direction of each loose hole. Therefore, it takes a relatively long time to find an appropriate position of the casing relative to the mount, at which a desired pump flow rate is achieved.
Thus, it is an objective of the present invention to provide a vane pump, which allows minimization of the time required to adjust a pump flow rate of the vane pump. It is another objective of the present invention to provide a method for adjusting a pump flow rate of such a vane pump. It is another objective of the present invention to provide a fuel vapor leakage check module having such a vane pump.
To achieve the objectives of the present invention, there is provided a vane pump that includes a motor arrangement, a rotor, a casing and at least one male threaded screw member. The motor arrangement includes a rotatable shaft and a support that rotatably supports the rotatable shaft. The rotor includes a plurality of vanes and is connected to the rotatable shaft. The casing includes a pump chamber and at least one elongated hole. The pump chamber receives the rotor in such a manner that the rotor is eccentric to the pump chamber. Each of the at least one elongated hole penetrates through the casing in a direction parallel to the rotatable shaft and has an elongated cross section. A major axis of the elongated cross section of each of the at least one elongated hole extends in a direction of eccentricity of the rotor relative to the pump chamber. Each of the at least one male threaded screw member is received through a corresponding one of the at least one elongated hole of the casing and each of which is threadably engaged with the support to connect the casing to the support. The casing holds each of the at least one male threaded screw member in a minor axial direction of the elongated cross section of a corresponding one of the at least one elongated hole to limit substantial movement of the male threaded screw member in the minor axial direction of the corresponding one of the at least one elongated hole.
To achieve the objectives of the present invention, there is also provided a method for adjusting a pump flow rate of the vane pump. According to the method, the pump flow rate of the vane pump is monitored, and at the same time, the casing is moved relative to the support in a state where the at least one male threaded screw member is loosened. Then, a position of the casing relative to the support is determined based on a result of the monitoring of the pump flow rate of the vane pump.
To achieve the objectives of the present invention, there is also provided a fuel vapor leakage check module for checking leakage of fuel vapor from a fuel tank. The fuel vapor leakage check nodule includes the vane pump. The fuel vapor leakage check module checks leakage of fuel vapor from the fuel tank through depressurization or pressurization of an interior of the fuel tank by the vane pump.